Heteroscorpionate Rare-Earth Catalysts for the Hydroalkoxylation

Article pubs.acs.org/Organometallics

Heteroscorpionate Rare-Earth Catalysts for the Hydroalkoxylation/ Cyclization of Alkynyl Alcohols Javier Martínez,† Antonio Otero,*,† Agustín Lara-Sánchez,*,† José Antonio Castro-Osma,† Juan Fernández-Baeza,† Luis F. Sánchez-Barba,‡ and Ana M. Rodríguez† †

Universidad de Castilla-La Mancha, Departamento de Química Inorgánica, Orgánica y Bioquímica, Instituto Regional de Investigación Científica Aplicada (IRICA), Centro de Innovación en Química Avanzada (ORFEO-CINQA), 13071 Ciudad Real, Spain ‡ Departamento de Biología y Geología, Física y Química Inorgánica, Universidad Rey Juan Carlos, Móstoles, 28933 Madrid, Spain S Supporting Information *

ABSTRACT: The chiral, enantiopure bis(pyrazol-1-yl)methane-based NNO-donor scorpionate ligands in the form of the alcohol compounds bpzbeH (bpzbe = 1,1-bis(3,5dimethylpyrazol-1-yl)-3,3-dimethyl-2-butoxide), bpzteH (bpzte = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-p-tolylethoxide), and (R,R)-bpzmmH ((R,R)-bpzmm = (1R)-1-{(1R)-6,6dimethylbicyclo[3.1.1]-2-hepten-2-yl}-2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide) have been used to obtain new NNOheteroscorpionate yttrium and lutetium complexes. The reactions of bpzbeH, bpzteH (racemic mixtures), and (R,R)bpzmmH (enantiopure compound) with [M{N(SiHMe2)2}3(thf)2] (M = Y, Lu) in a 1:1 molar ratio in toluene afforded the mononuclear bis(silylamide) complexes [M{N(SiHMe2)2}2(κ3-NNO)(thf)] (M = Y, Lu; 1−6), respectively. When the reaction was carried out with a 2:1 molar ratio (ligand to metal precursor) or with excess ligand, homoleptic complexes of the type [Y(κ3NNO)2(κ-O-NN)] (κ3-NNO = κ-O-NN = bpzbe (7), bpzte (8)) were obtained. Compounds 1 and 3 were used as convenient starting materials for the synthesis of the aryloxide and alkoxide yttrium compounds [Y(OR)2(κ3-bpzbe)] (OR = O-2,6-Me2C6H3 (9), O-CH2(2-CHC)C6H4 (10)) and [Y(OR)2(κ3-bpzte)] (OR = O-2,6-Me2C6H3 (11), O-CH2(2-CHC)C6H4 (12)). The structures of the complexes were determined by spectroscopic methods, and the X-ray crystal structures of 1, 2, and 7 were also established. Complexes 1−6 are efficient catalysts for the intramolecular hydroalkoxylation of alkynyl alcohols and give TOF values up to 19.4 h−1 at 90 °C for (2-ethynylphenyl)methanol (13) by using the single enantiopure complex 5 as catalyst, producing exclusively the exo-methylene products. The activation parameters ΔH⧧ = 19.93(0.2) kcal/mol, ΔS⧧ = −28.75(0.2) eu, and Ea = 18.61(0.2) kcal/mol are consistent with observations for other catalyst-mediated insertive hydroelementation processes.

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INTRODUCTION The hydroalkoxylation of C−C multiple bonds is a prominent and highly atom efficient reaction for the synthesis of oxygencontaining compounds.1 In particular, oxygen-containing heterocycles have applications in the pharmaceutical and fine chemicals industries.1,2 In recent years, several research groups have focused their efforts toward intramolecular cyclohydroalkoxylation of different unsaturated alcohol compounds (alkynyl alcohol, alkenyl alcohol, allenyl alcohol), developing both new methods of heterocycle synthesis and a better understanding of these synthetic processes.3 This catalytic addition of an O−H σ bond to unsaturated carbon−carbon bonds allows the preparation of complex oxygen-containing compounds in a waste-free, highly atom economical manner starting from simple and inexpensive starting materials. A staggering number of catalytic systems have been developed for this reaction, and these exhibit a correspondingly high degree of mechanistic diversity.1−6 For the intramolecular alkynyl alcohol hydroalkoxylation, two possible regioisomers can be envisioned as © XXXX American Chemical Society

reaction products (Scheme 1), and both the exo-dig and the endo-dig cyclizations are possible to yield tetrahydrofurans or dihydropyran products according to Baldwin’s rules.7 In particular, the intramolecular hydroalkoxylation of a variety of carbon−carbon unsaturations such as alkynes, alkenes, and allenes using group 3 and rare-earth-metal complexes has recentely been reported by Marks and coworkers.8 It has been established that this process involves an Scheme 1. The Two Possible Regioisomers for the Intramolecular Cyclization of Alkynyl Alcohols

Received: March 10, 2016

A

DOI: 10.1021/acs.organomet.6b00203 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

catalytic activity comparable to that of the other rare-earth systems. Herein, we describe in detail the synthesis and characterization of a series of chiral heteroscorpionate amido and alkoxide yttrium and lutetium complexes, some of which are enantiopure compounds. The performance of these complexes in the hydroalkoxylation/cyclization of commercial alkynyl alcohols was explored under well-controlled conditions.

intramolecular insertion of the unsaturated substrate into a metal−alkoxide bond8 via a four-centered transition state, followed by a rapid protonolysis of the intermediate lanthanide−carbon species formed by alcohol substrates to yield the oxygen-heterocyclic product and regenerate the catalytically active species (Figure 1). This is a mechanistic scenario similar to that established for hydroamination and hydrophosphination catalysis mediated by organolanthanide catalysts.9

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RESULTS AND DISCUSSION Syntheses and Structural Characterization. The synthesis of the yttrium and lutetium bis(silylamide) complexes [M{N(SiHMe2)2}2(κ3-bpzbe)(thf)] (M = Y (1), Lu (2)), [M{N(SiHMe2)2}2(κ3-bpzte)(thf)] (M = Y (3), Lu (4)), and [M{N(SiHMe2)2}2(κ3-R,R-bpzmm)(thf)] (M = Y (5), Lu (6)) was achieved through a protonolysis reaction involving amine elimination. Thus, the reaction of bpzbeH,11g bpzteH11g (racemic mixtures), or (R,R)-bpzmmH11g (enantiopure compound) with [M{N(SiHMe2)2}3(thf)2]15 (M = Y, Lu) in a 1:1 molar ratio in toluene at low temperature afforded, after the appropriate workup, the yttrium and lutetium diamide complexes 1−6 as white solids in ca. 80% yield (Scheme 2). Scheme 2. Synthesis of Yttrium and Lutetium Complexes 1− 8

Figure 1. Proposed σ-bond insertion mechanism for intramolecular hydroalkoxylation.

The development of new lanthanide (group 3 and rare earth) metal based hydroalkoxylation catalysts with higher activity and selectivity, including chiral catalysts for enantioselective hydroalkoxylation, and systems bearing ancillary ligands that permit facile tuning of catalytic properties through adjustment of their steric and electronic features has remained a challenge. Heteroscorpionates are among the most versatile types of tridentate ligands, and they can coordinate to a wide variety of elements.10 Chemistry based on the design of this particular type of intriguing ligand has been extended considerably in terms of coordination chemistry11 and catalytic applications.12 In the past decade, a number of research groups have contributed widely to this field by designing new ligands related to the bis(pyrazol-1-yl)methane system and incorporating several pendant donor arms.13 Some of us reported the use of alkyl heteroscorpionate rare-earth complexes as efficient precatalysts for intramolecular hydroamination of aminoalkenes.14 Thus, bearing in mind both the versatility of this type of tridentate monoanionic ligand and the efficiency of rareearth-catalyzed hydrofunctionalization processes, we decided to develop hydroalkoxylation catalysts based on heteroscorpionate ligands. It was envisaged that these compounds would have

Complexes 5 and 6 were obtained as single enantiopure compounds. When the reaction of [M{N(SiHMe2)2}3(thf)2] with the heteroscorpionate precursors was carried out in a 1:2 or 1:3 molar ratio, under the same reaction conditions, a mixture of complexes was obtained, from which the homoleptic yttrium complexes [Y(κ3-bpzbe)2(O-bpzbe)] (7) and [Y(κ3bpzte)2(O-bpzte)] (8) could be isolated and characterized (Scheme 2). Complexes 7 and 8 were obtained as white solids in low yield (25%). The different complexes were characterized by spectroscopic methods. The Si−H stretching frequencies in the FTIR spectra of 1−6 in the solid state are in the region between 1900 and 2200 cm−1, with low-energy shoulders, and this indicates the presence of weak agostic β-(Si−H) interactions in the solid state.16 Hovewer, conclusive evidence was not found for the presence of β-(Si−H) agostic interactions in compounds 1−6 in solution, a situation that is frequently observed in similar B


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Organometallics

Figure 2. ORTEP drawings of compounds 1 (a) and 2 (b). Ellipsoids are given at the 30% probability level, and hydrogen atoms have been omitted for clarity.

complexes.16 Thus, the values of the 1JSiH coupling constants for these complexes are in the range that is indicative of nonagostic interactions (175−180 Hz) observed for rare-earth complexes.16 The 1H and 13C{1H} NMR spectra of 1−6 exhibit two distinct sets of pyrazole resonances, indicating the existence of two types of pyrazole rings. The 1H NMR spectra of these complexes show two singlets for the H4, Me3, and Me5 pyrazole protons, one broad singlet for the Si−H protons, and two sets of signals for the SiMe2 protons and the “R” moieties of the heteroscorpionate ligands. The results are consistent with an octahedral environment for the metal atoms in which the thf ring is located in trans positions with respect to the oxygen atom (see Scheme 2). The 1H NOESY-1D experiments permitted the unequivocal assignment of all 1H resonances, and the assignment of the 13C{1H} NMR signals was made on the basis of 1H−13C heteronuclear correlation (g-HSQC) experiments. The NMR spectra of homoleptic complexes 7 and 8 confirm the loss of the three silylamide ligands [N(SiHMe2)2] from the [Y{N(SiHMe2)2}3(thf)2] precursors and contain broad signals for the different protons and carbons. The molecular structures of complexes 1, 2, and 7 were determined by X-ray diffraction studies. The ORTEP drawings for complexes 1 and 2 are depicted in Figure 2. The crystals of complexes 1 and 2 contain a racemic mixture, and the structures of the (S)-1 and (R)-2 enantiomers are depicted in Figure 2. The crystallographic data and selected interatomic distances and angles are given in Table S1 in the Supporting Information and Table 1, respectively. The molecular structures of 1 and 2 are in good agreement with the solution structures deduced from the spectroscopic data. The heteroscorpionate ligand is attached to the yttrium or lutetium atom through two nitrogen atoms of pyrazole rings and the oxygen atom in a κ3-NNO coordination mode, which has the expected fac coordination fashion. In addition, the yttrium or lutetium center is coordinated to two silylamide ligands and to a thf ring in a slightly distorted octahedral geometry. This distortion is manifested in the angles N(1)− Y(1)−N(5) = 156.4(2)° and O(1)−Y(1)−O(2) = 149.4(1)° for 1 and N(3)−Lu(1)−N(5) = 157.5(1)° and O(1)−Lu(1)− O(2) = 151.2(1)° for 2. The M−N bond distances from the silylamide ligands range from 2.252(4) to 2.304(4) Å and correlate well with the corresponding distances found in other

Table 1. Bond Lengths (Å) and Angles (deg) for 1 and 2 1

Y(1)−O(1) Y(1)−O(2) Y(1)−N(1) Y(1)−N(3) Y(1)−N(5) Y(1)−N(6) Y(1)−Si(2) Y(1)−Si(3) O(1)−Y(1)−O(2) N(6)−Y(1)−N(3) N(5)−Y(1)−N(1) C(12)−O(1)−Y(1)

2 Bond Lengths (Å) 2.079(4) Lu(1)−O(1) 2.431(4) Lu(1)−O(2) 2.595(5) Lu(1)−N(5) 2.572(5) Lu(1)−N(6) 2.293(4) Lu(1)−N(1) 2.304(4) Lu(1)−N(3) 3.437(2) Lu(1)−Si(1) 3.316(2) Lu(1)−Si(3) Bond Angles (deg) 149.4(1) O(1)−Lu(1)−O(2) 166.3(2) N(6)−Lu(1)−N(1) 156.4(2) N(5)−Lu(1)−N(3) 137.8(3) C(12)−O(1)−Lu(1)

2.057(3) 2.373(3) 2.252(4) 2.258(4) 2.527(3) 2.546(4) 3.378(1) 3.299(1) 151.2(1) 167.3(1) 157.5(1) 136.7(3)

yttrium and lutetium amide complexes.17 These bond lengths are shorter than the M−N bond distances from the pyrazole ring (2.527(3)−2.595(5) Å). The M−O(1) bond lengths, Y(1)−O(1) = 2.079(4) Å and Lu(1)−O(1) = 2.057(3) Å, are shorther than the M−O(2) bonds, Y(1)−O(2) = 2.431(4) Å and Lu(1)−O(2) = 2.373(3) Å, thus confirming that this oxygen atom is bonded to the metal center in an anionic fashion. The molecular structures of 1 and 2 show the presence of weak asymmetric β-(Si−H) monoagostic interactions of the silylamide ligand (for complex 1, Si(3)−H(3I)···Y(1); for complex 2, Si(3)−H(3I)···Lu(1)) (Table S2).15,18 The close M···Si contacts, Y(1)−Si(3) = 3.316(2) Å and Lu(1)−Si(3) = 3.298(1) Å, are shorter than the Y(1)−Si (3.437(2)−3.591(2) Å) and Lu(1)−Si (3.379(2)−3.547(2) Å) distances, respectively, and they are similar to the Y or Lu−Si σ-bond distances.15,18 These data suggest an interaction in the solid state. Furthermore, the close Y···H and Lu···H interactions, Y(1)−H(3I) = 3.21(5) Å and Lu(1)−H(3I) = 3.32(6) Å (Table S2 in the Supporting Information), complete the formation of agostically fused M−N−Si−H four-membered rings. The weak agostic M···SiH interactions cause a slight contraction of the M−N−Si angles, Si(3)−N(6)−Y(1) = C


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Organometallics 111.6(2)° and Si(3)−N(6)−Lu(1) = 112.3(2)°, which correspond to the M···Si contacts. The formulation for the homoleptic complexes was confirmed by X-ray structural analyses on compound 7. This complex crystallizes with two molecules per unit cell. A view of the molecular structure is shown in Figure 3. The crystal

Scheme 3. Synthesis of Yttrium Aryloxide and Alkoxide Complexes 9−12

clearly show the resonance for the alkynyl proton (Figure 4). Complexes 11 and 12 could be the M−O active species formed by activation of the silylamide heteroscorpionate precatalysts by protonolysis of the silylamide ligands in hydroalkoxylation/ cyclization processes of alkynyl alcohols.8 Catalytic Hydroalkoxylation Studies. Complexes 1−6 were tested in the catalytic intramolecular hydroalkoxylation/ cyclization of alkynyl alcohols. These complexes were active for the hydroamination/cyclization of various alkynyl alcohol derivatives (see Table 2). The catalytic activity was monitored by 1H NMR spectroscopy by loading an NMR tube with catalyst and substrate and heating the reaction mixtures to different temperatures. The reactivities of the catalysts were tested in the hydroalkoxylation of (2-ethynylphenyl)methanol (13).8 The silylamide compounds 1−6 served as effective precatalysts for the quantitative intramolecular hydroalkoxylation of 13 to give the corresponding furan 14 at 90 °C, under an inert atmosphere, at 5 mol % catalyst loading and with short reaction times (Table 2). Enantiopure complexes 5 and 6 showed the highest catalytic activity (Table 2), although due to the substrate scope used (alkynyl alcohols), no enantioasymmetric process is observed. The progress of the reaction was monitored by intensity changes in the olefinic resonances of the substrate by 1H NMR spectroscopy, using evolved HN(SiHMe2)2 or added Ph3SiMe as an internal NMR standard (Figure 5). The catalytic activities of yttrium complexes 1, 3, and 5 in the hydroalkoxylation of substrate 13 were higher in comparison to those of the lutetium complexes 2, 4, and 6 and followed the general trend shown by lanthanide-mediated hydroelementation.8 A positive effect of the temperature and catalyst loading on the catalyst activity was observed (Table 2, entries 1−10). The benzofuran 14 was formed cleanly by 5-exo cyclization and there was no evidence for the alternative 6-endo cyclization. A strong dependence of structural effects on this catalytic transformation, including five- and six-membered-ring formation, was observed on using two primary alcohols. Entries 11− 16 (Table 2) correspond to the results obtained in the hydrolkoxylation/cyclization of pent-4-yn-1-ol (15) and hex-5yn-1-ol (17), which do not bear a substituent on the carbon backbone. For these substrates the catalytic activity was lower than for 13, probably due to some combination of the significant Thorpe−Ingold19 effect and electronic factors of the arene substituted in substrate 13 (Table 2, entries 11−16) (see for example a comparison of TOF values, entry 2 versus 12 or entry 3 versus 13). For these cyclization reactions much longer reaction times and higher temperatures were required to obtain high or medium yields.

Figure 3. ORTEP drawing of compound 7. Ellipsoids are given at the 30% probability level, and hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Y(1)−O(1) 2.123(3), Y(1)−O(2) 2.151(3), Y(1)−O(3) 2.175(3), Y(1)−N(1) 2.833(4), Y(1)−N(3) 2.623(4), Y(1)−N(5) 2.665(4), Y(1)−N(7) 2.513(4); O(1)−Y(1)−N(7) 148.0(1), O(1)−Y(1)−O(2) 119.0(1), O(2)−Y(1)−O(3) 81.4(1).

contains a racemic mixture of single diastereoisomers (S,S,R + R,R,S), and the structure of the R,R,S enantiomer is depicted in Figure 3. Crystallographic data and selected interatomic distances and angles are given in Table S1 in the Supporting Information and in the caption for Figure 3, respectively. Complex 7 is seven-coordinate and has a distorted-pentagonalbipyramidal metal coordination sphere, with the major distortion in the angle O(1)−Y(1)−N(7) of 148.0 (1)°. The yttrium center is out of the equatorial plane defined by N(1), N(3), O(3), O(2), and N(5) by 0.12 Å. The average Y− Npyrazole and Y−O distances, 2.658(4) and 2.150(3) Å, respectively, are longer than those in 1, 2.583(5) and 2.079(4) Å, owing to the steric demands of complex 7. With the aim of testing the silylamide complexes 1−6 for catalytic intramolecular hydroalkoxylation processes, we studied the reaction of some of these complexes with different alcohols such as 2,6-dimethylphenol and (2-ethynylphenyl)methanol. The addition of 2 equiv of the alcohols to the silylamide compounds 1 and 3 in toluene at room temperature gave the aryloxide and alkoxide species [Y(OR)2(κ3-bpzbe)] (OR = O2,6-Me2C6H3 (9), O-CH2(2-CHC)C6H4 (10)) and [Y(OR)2(κ3-bpzte)] (OR = O-2,6-Me2C6H3 (11), O-CH2(2CHC)C6H4 (12)). Complexes 9−12 were isolated as white solids in good yields (Scheme 3). The complexes were characterized by spectroscopic methods. The 1H and 13C{1H} NMR spectra of 9−12 at room temperature show two sets of resonances for the pyrazole protons and carbons, indicating that the pyrazoles are not equivalent, along with the resonances for the aryloxide or alkoxide moieties. The 1H NMR spectra for complexes 11 and 12, which contain the (2-ethynylphenyl)methoxide moiety, D


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Figure 4. 1H NMR spectrum of the complex [Y{O-CH2(2-CHC)C6H4}2(κ3-bpzte)(thf)] (12) in CDCl3.

substrate concentration versus time (Figure 6) were obtained for experiments carried out at [13] = 0.20−0.67 M, and these indicate a zero-order rate dependence on substrate concentration (a = 0). Furthermore, the order with respect to the concentration of catalyst 3 was investigated by carrying out a set of reactions at four different concentrations of this complex, with the concentration of substrate 13 kept constant at [13] = 0.286 M. The plot of kobs versus [3] showed a good fit to a straight line (Figure 7a), and this indicates that the reaction is first-order in catalyst concentration. This finding was confirmed by a plot of log [3] versus log kobs (Figure 7b), which showed a slope of 0.94 and verified that the reaction is first-order with respect to the concentration of 3 (b = 1). Therefore, the rate equation for the hydroalkoxylation/cyclization of primary terminal alkynyl alcohols catalyzed by complex 3 can be expressed by eq 2.

As observed for the organolanthanide catalyst mediated hydroamination/cyclization,20 the ring-size dependence of cyclization rates (TOF) for the present primary alkynyl alcohols is 5 > 6, which is consistent with a classical, stereoelectronic cyclization process (Table 2, entries 11−13 versus 14−16).21 The final furan, benzofuran, and pyran products were vacuum-transferred and purified. The products were characterized by NMR spectroscopy and elemental analysis (see the Supporting Information). With the TMSsubstituted internal alkyne 19 the hydroalkoxylation/cyclization reaction did not proceed, even after 1 week at 120 °C. Several products, together with alkynyl alcohol 19, were detected by 1H NMR spectroscopy (see Figure S1 in the Supporting Information). In order to gain an insight into the proposed general mechanism for the lanthanide-catalyzed hydroalkoxylation, we investigated the stoichiometric reaction of 3 with the substrate 19 on a preparative scale in toluene as solvent at room temperature (Scheme 4). The clean formation of the dialkoxide yttrium compound [Y{O-(CH 2 ) 3 -(CC)TMS}2(κ3-bpzbe)] (21) was observed, and the compound was characterized spectroscopically. The dialkoxide yttrium product 21 was observed when the catalytic cyclization reaction of substrate 19 with 3 as catalyst was carried out (see Figure S2 in the Supporting Information). The formation of 11, 12, and 19 is consistent with the mechanism proposed for the hydroalkoxylation/cyclization of alkynyl alcohols with our precatalysts (Figure 1). In fact, reaction of complex 3 with 2 equiv of 13 or 19 would lead to the transient bis-alkoxide species, step A, through a protonolysis process. Kinetic Studies. Kinetic studies on the hydroalkoxylation/ cyclization reaction of (2-ethynylphenyl)methanol (13) using complex 3 as catalyst were carried out at 90 °C in toluene-d8. Reactions were monitored in situ by 1H NMR spectroscopy (see the Supporting Information). The general rate equation for this reaction can be written as shown in eq 1. rate = k[13]a [3]b

rate = kobs[13]0 [3]1

(2)

This empirical rate law is typical of the kinetics for the lanthanide-catalyzed hydroalkoxylation/cyclization of primary terminal alkynyl alcohols, which show zero-order dependence of the reaction rate on the concentration of substrate and firstorder dependence of the reaction rate on the concentration of catalyst. Equation 2 has the same form as that previously reported by Marks and co-workers for the hydroalkoxylation/ cyclization of terminal alkynyl alcohols mediated by lanthanide catalysts.8 Activation Parameters. Having determined the order with respect to substrate 13 and catalyst 3, a variable-temperature kinetics study was undertaken in order to determine the activation parameters for the cyclization of (2-ethynylphenyl)methanol in toluene. Reactions were carried out at five temperatures between 50 and 90 °C, and these were monitored in situ by 1H NMR spectroscopy. The rate of substrate consumption was constant, and this indicates that the reaction is zero-order with respect to the concentration of substrate 13 (Figure 8). The corresponding Arrhenius plot is shown in Figure 9. The energy of activation (Ea) can be obtained from the slope of the data plotted in Figure 9, and it was found to be 18.61(0.2) kcal/ mol. The activation energy for catalyst 3 was similar to the Ea

(1)

The order with respect to the concentration of substrate 13 was studied by carrying out a set of reactions at four different concentrations of this substrate, with the concentration of complex 3 kept constant at [3] = 0.014 M. Linear plots of E


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are cleaved to generate the product and simultaneously regenerate the M−O active moieties (Figure 1, step C).

Table 2. Catalytic Intramolecular Hydroalkoxylation/ Cyclization Reactions of Primary Terminal Alkynyl Alcohols by Complexes 1−6

entry cat. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 a

1 3 5 2 4 6 3 5 3 5 1 3 5 1 3 5 3 5

substrate

[cat.]/ [substrate] (%)

T (°C)

t (h)

yield (%)a

TOF (h−1)

13 13 13 13 13 13 13 13 13 13 15 15 15 17 17 17 19 19

5 5 5 5 5 5 5 5 1 1 5 5 5 5 5 5 5 5

90 90 90 90 90 90 60 60 90 90 90 90 90 120 120 120 120 120

2.0 2.0 1.0 2.5 2.3 1.7 3.8 1.6 9.2 5.4 7.0 6.5 3.0 24.0 24.0 24.0 168.0 168.0

95 98 97 98 99 99 98 96 98 98 95 98 96 45 43 53 0 0

9.5 9.8 19.4 7.8 8.6 11.6 5.1 11.2 2.1 3.6 2.7 3.0 6.4 0.3 0.3 0.4 0 0

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CONCLUSIONS In conclusion, we report here a facile synthesis of a new family of bis(silylamide) and alkoxide heteroscorpionate yttrium and lutetium compounds bearing alkoxide groups as pendant donor arms. Some of the complexes were obtained as single enantiopure compounds (5 and 6). These complexes promoted efficiently the intramolecular hydroalkoxylation of several alkynyl alcohols. The alkoxide yttrium complexes 11, 12, and 21 have been isolated and characterized by stoichiometric reaction of 1 or 3 with the substrate 13 or 19. The formation of these compounds is consistent with the general insertion mechanism for lanthanide metal catalysts, and they must evolve from a bis-alkyl key catalytic intermediate resulting from an insertion step of a CC moiety into a few reactive metal− alkoxide bonds. The activation parameters ΔH⧧ = 19.93(0.2) kcal/mol, ΔS⧧ = −28.75(0.2) eu, and Ea = 18.61(0.2) kcal/mol closely follow the trends observed for related lanthanide insertive hydroelementation processes. Further studies are being carried out in order to examine thoroughly the effect of changes to both the rare-earth-metal center and the scorpionate ligand framework on the catalytic activity of complexes in hydroalkoxylation processes and to expand on the alkynyl alcohol substrate scope examined in the present study.

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EXPERIMENTAL SECTION

All preparations and subsequent manipulations were carried out using drybox and standard Schlenk techniques under an atmosphere of dinitrogen. Solvents were predried over sodium wire (toluene, nhexane) and distilled under nitrogen from sodium (toluene) or sodium−potassium alloy (n-hexane). Deuterated solvents were stored over activated 4 Å molecular sieves and degassed by several freeze− thaw cycles. IR spectra were obtained on a Shimadzu IR Prestige-21 spectrophotometer equipped with a Pike Technology ATR system. Microanalyses were carried out on a PerkinElmer 2400 CHN analyzer. 1 H, 13C, and 29Si NMR spectra were recorded on a Varian Inova FT500 spectrometer and referenced to the residual deuterated solvent. The specific rotation [α]D22 was measured at 22 °C on a PerkinElmer 241 polarimeter equipped with a sodium lamp operating at 589 nm with a light path length of 10 cm. YCl3 and LuCl3 were used as purchased (Aldrich or Strem). 2,6-Dimethylphenol, (2ethynylphenyl)methanol (13), pent-4-yn-1-ol (15), hex-5-yn-1-ol (17), and 5-(trimethylsilyl)pent-4-yn-1-ol (19) were purchased from Aldrich. The compounds [M{N(SiHMe2)2}3(thf)2]15 (M = Y, Lu), bpzbeH,11g bpzteH,11g and (R,R)-bpzmmH11g were prepared according to literature procedures. Synthesis of [Y{N(SiHMe2)2}2(κ3-bpzbe)(thf)] (1). A solution of bpzbeH (0.23 g, 0.79 mmol) in toluene (20 mL) was added dropwise to a solution of [Y(N(SiHMe2)2)3(thf)2] (0.50 g, 0.79 mmol) in toluene (20 mL) at −70 °C. The reaction mixture was warmed to room temperature and stirred for 2 h. Evaporation of the solvent gave a white solid. The solid was recrystallized from toluene/hexane (10/1, 20 mL at −20 °C) to give white crystals of compound 1. Yield: 0.43 g, 77%. Anal. Calcd for C28H61N6O2Si4Y: C, 47.03; H, 8.60; N, 11.75. Found: C, 47.15; H, 8.74; N, 11.49. IR (cm−1): ν 2018 [vs, ν(SiH)], 1976 (m, sh), 1560 [s, ν(CN)]. 1H NMR (500 MHz, C6D6, 297 K): δ 6.07 (s, 1 H, CH), 5.55 (s, 1 H, H4′), 5.51 (s, 1H, H4), 5.25 (br s, 4H, SiHMe2), 3.96 (s, 1 H, CHa), 3.79 (m, 4H, THF), 2.49 (s, 3H, Me3′), 2.46 (s, 3H, Me3), 1.79 (s, 3H, Me5′), 1.73 (s, 3H, Me5), 1.36 (m, 4 H, THF), 0.90 [s, 9H, C(CH3)], 0.58 (d, 3JHH = 2.9 Hz, 12H, SiHMe2), 0.55 (d, 3JHH = 3.0 Hz, 12H, SiHMe2). 13C{1H} NMR (125 MHz, C6D6, 297 K): δ 150.0, 149.8, 139.0, 137.8 (C3,3′, C5,5′), 106.6 (CH4′), 106.1 (CH4), 86.9 (CHa), 70.3 (THF), 66.7 (CH), 36.1 [C(CH3)], 26.6 [C(CH3)], 25.3 (THF), 14.8 (Me3′), 14.8 (Me3), 11.5

Yield determined by 1H NMR spectroscopy.

data for other lanthanide complexes.8 The enthalpy of activation (ΔH⧧) and entropy of activation (ΔS⧧) were obtained from the slope and the y-axis intercept, respectively, of the Eyring plot (Figure S12 in the Supporting Information).22 The ΔH⧧ and ΔS⧧ values obtained were 19.93(0.2) kcal/mol and −28.75(0.2) eu, respectively. The activation parameters for catalyst 3 were of the same order as those of lanthanide catalysts for the hydroalkoxylation/ cyclization reaction of alkynyl alcohols.8 A detailed mechanistic study was carried out on these systems, and it was established that the process involves the intramolecular insertion of the unsaturated substrate into the metal−alkoxide bond (Figure 1).8 The precatalyst is activated by protonolysis of the silylamide bonds, and the active M−OR catalytic species is generated (Figure 1, step A). The alkyne moieties subsequently approach and undergo insertions into the M−O bonds via a four-center transition state (Figure 1, step B).23 This is the most thermodynamically demanding step and is also the turnover-limiting step in the catalytic cycle. The generated M−C bonds are highly reactive to protonolysis and F


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Organometallics

Figure 5. 1H NMR monitoring (500 MHz) of the hydroalkoxylation of 13 to 14 mediated by the [Y{N(SiHMe2)2}2(κ3-bpzte)(thf)] (3) precatalyst in toluene at 80 °C from 0 to 2.5 h.

Scheme 4. Synthesis of Dialkoxide Yttrium Complex 21 from the Stoichiometric Reaction of 3 with 19

Synthesis of [Lu{N(SiHMe2)2}2(κ3-bpzbe)(thf)] (2). The synthesis of 2 was carried out in a manner identical with that for 1, using bpzbeH (0.21 g, 0.70 mmol) and [Lu(N(SiHMe2)2)3(thf)2] (0.50 g, 0.70 mmol) to give 2 as a white solid. Yield: 0.51 g, 91%. Anal. Calcd for C28H61LuN6O2Si4: C, 41.98; H, 7.67; N, 10.49. Found: C, 42.08; H, 7.84; N, 10.22. IR (cm−1): ν 2034 [vs, ν(SiH)], 1988 (m, sh), 1565 [s, ν(CN)]. 1H NMR (500 MHz, C6D6, 297 K): δ 6.01 (s, 1H, CH), 5.49 (s, 1 H, H4′), 5.46 (s, 1H, H4), 5.15 (br s, 4H, SiHMe2), 4.00 (s, 1 H, CHa), 3.78 (m, 4H, THF), 2.49 (s, 3H, Me3), 2.44 (s, 3H, Me3′), 1.72 (s, 3H, Me5′), 1.66 (s, 3H, Me5), 1.38 (m, 4 H, THF), 0.88 [s, 9H, C(CH3)], 0.60, 0.57 (br s, 12H, 12H, SiHMe2). 13C{1H} NMR (125 MHz, C6D6, 297 K): δ 149.8, 148.9, 139.0, 137.2 (C3,3′, C5,5′), 106.4 (CH4′), 106.0 (CH4), 86.9 (CHa), 68.8 (THF), 66.8 (CH), 35.9 [C(CH3], 26.3 [C(CH3)], 25.2 (THF), 14.5 (Me3,3′), 11.1 (Me5′), 10.6 (Me5), 4.1 (SiHMe2), 4.0 (SiHMe2). 29Si NMR (99.5 MHz, C6D6, 297 K): δ −22.8 (ds, 1JSiH = 175.5 Hz, 2JSiH = 8.1 Hz, NSiHMe2). Synthesis of [Y{N(SiHMe2)2}2(κ3-bpzte)(thf)] (3). The synthesis of 3 was carried out in in a manner identical with that for 1, using bpzteH (0.26 g, 0.79 mmol) and [Y(N(SiHMe2)2)3(thf)2] (0.50 g, 0.79 mmol) to give 3 as a white solid. Yield: 0.51 g, 86%. Anal. Calcd

Figure 6. Linear regresion fits for [(2-ethynylphenyl)methanol] versus time, indicating that the reactions are zero-order in substrate concentration. The concentration of catalyst 3 was 0.014 M. (Me5′), 11.0 (Me5), 4.4 (SiHMe2), 4.2 (SiHMe2). 29Si NMR (99.5 MHz, C6D6, 297 K): δ −23.5 (ds, 1JSiH = 177.5 Hz, 2JSiH = 8.3 Hz, NSiHMe2). G


Article

Organometallics

3H, Me3), 2.17 (s, 3H, MePh), 1.67 (s, 3H, Me5′), 1.36 (m, 4H, THF), 1.21 (s, 3H, Me5), 0.61 (d, 3JHH = 2.5 Hz, 12H, SiHMe2), 0.59 (d, 3JHH = 2.4 Hz, 12H, SiHMe2). 13C{1H} NMR (125 MHz, C6D6, 297 K): δ 149.9, 149.4, 141.8, 140.4, 139.1, 137.5 (C3,3′, C5,5′, Cipso,p-MePh), 128.9 (Cm-MePh), 126.3 (Co-MePh), 106.0 (CH4′), 105.3 (CH4), 80.7 (CHa), 72.4 (CH), 69.5 (THF), 25.1 (THF), 21.0 (MePh), 14.5 (Me3′), 14.4 (Me3), 10.6 (Me5′), 10.0 (Me5), 4.0 (SiHMe2), 3.7 (SiHMe2). 29Si NMR (99.5 MHz, C6D6, 297 K): δ −22.6 (ds, 1JSiH = 176.3 Hz, 2JSiH = 8.2 Hz, NSiHMe2). Synthesis of [Lu{N(SiHMe2)2}2(κ3-bpzte)(thf)] (4). The synthesis of 4 was carried out in in a manner identical with that for 1, using bpzteH (0.23 g, 0.70 mmol) and [Lu(N(SiHMe2)2)3(thf)2] (0.50 g, 0.70 mmol) to give 4 as a white solid. Yield: 0.53 g, 92%. Anal. Calcd for C31H59LuN6O2Si4: C, 44.58; H, 7.12; N, 10.06. Found: C, 44.67; H, 7.04; N, 10.28. IR (cm−1): ν 2019 [vs, ν(SiH)], 1974 (m, sh), 1559 [s, ν(CN)]. 1H NMR (500 MHz, C6D6, 297 K): δ 7.29 (d, 3JHH = 7.4 Hz, 2H, Ho-MePh), 7.11 (d, 3JHH = 7.4 Hz, 2H, HmMePh), 6.82 (s, 1H, CH), 5.62 (s, 1H, CHa), 5.54 (s, 1H, H4′), 5.36 (s, 1H, H4), 5.25 (m, 4H, SiHMe2), 3.81 (m, 4H, THF), 2.50 (s, 3H, Me3′), 2.48 (s, 3H, Me3), 2.12 (s, 3H, MePh), 1.63 (s, 3H, Me5′), 1.36 (m, 4H, THF), 1.19 (s, 3H, Me5), 0.63 (d, 3JHH = 3.0 Hz, 12H, SiHMe2), 0.61 (d, 3JH−H = 3.0 Hz, 12H, SiHMe2). 13C{1H} NMR (125 MHz, C6D6, 297 K): δ 150.1, 149.6, 140.2, 139.0, 137.5, 136.3 (C3,3′, C5,5′, Cipso,p-MePh), 129.2 (Cm-MePh), 126.4 (Co-MePh), 106.3 (C4′), 105.5 (C4), 81.0 (CHa), 72.9 (CH), 68.8 (THF), 25.2 (THF), 21.0 (MePh), 14.6 (Me3′), 14.4 (Me3), 10.6 (Me5′), 10.0 (Me5), 4.1 (SiHMe2), 3.9 (SiHMe2). 29Si NMR (99.5 MHz, C6D6, 297 K): δ −22.7 (ds, 1JSiH = 177.3 Hz, 2JSiH = 8.4 Hz, NSiHMe2). Synthesis of [Y{N(SiHMe2)2}2(κ3-R,R-bpzmm)(thf)] (5). The synthesis of 5 was carried out in in a manner identical with that for 1, using (R,R)-bpzmmH (0.23 g, 0.79 mmol) and [Y(N(SiHMe2)2)3(thf)2] (0.50 g, 0.79 mmol) to give 5 as a white solid. Yield: 0.55 g, 90%. Anal. Calcd for C33H65N6O2Si4Y: C, 50.87; H, 8.41; N, 10.79. Found: C, 50.95; H, 8.59; N, 10.49. [α]D25 = 25.1 (c 10−3 g/ mL, toluene). IR (cm−1): ν 2041 [vs, ν(SiH)], 1991 (m, sh), 1541 [s, ν(CN)]. 1H NMR (500 MHz, C6D6, 297 K): δ 5.85 (s, 1H, CH), 5.55 (br s, 1H, CHa), 5.46 (s, 1H, H4′), 5.37 (s, 1H, H4), 5.23 (m, 4H, SiHMe2), 4.95 (s, 1H, CHc), 3.78 (m, 4H, THF), 2.47 (s, 3H, Me3′), 2.44 (s, 3H, Me3), 2.24 (m, 4H, Hd,e,h), 2.10 (br s, 2H, Hg), 1.75 (s, 3H, Me5′), 1.67 (s, 3H, Me5), 1.38 (m, 4H, THF), 1.31, 0.98 (s, 6H, Mei,j), 0.57 (br s, 12H, SiHMe2), 0.51 (br s, 12H, SiHMe2). 13C{1H} NMR (125 MHz, C6D6, 297 K): δ 152.4, 150.0, 139.4, 138.9, 137.5 (C3,3′, C5,5′,Cb), 117.5 (Cc), 106.0 (CH4′), 105.8 (CH4), 81.4 (CHa), 71.4 (CH), 69.4 (THF), 59.4 (Cf), 41.5, 40.7, 37.9 (Cd,e,h), 31.9 (Cg), 26.0, 21.0 (Mei,j), 25.2 (THF), 14.5 (Me3′), 13.4 (Me3), 11.0 (Me5′), 10.6 (Me5), 3.8 (SiHMe2), 3.6 (SiHMe2). 29Si NMR (99.5 MHz, C6D6, 297 K): δ −23.1 (ds, 1JSiH = 177.8 Hz, 2JSiH = 8.5 Hz, NSiHMe2). Synthesis of [Lu{N(SiHMe2)2}2(κ3-R,R-bpzmm)(thf)] (6). The synthesis of 6 was carried out in in a manner identical with that for 1, using (R,R)-bpzmmH (0.25 g, 0.70 mmol) and [Lu(N(SiHMe2)2)3(thf)2] (0.50 g, 0.70 mmol) to give 6 as a white solid. Yield: 0.53 g, 88%. Anal. Calcd for C33H65LuN6O2Si4: C, 45.81; H, 7.57; N, 9.71. Found: C, 45.97; H, 7.69; N, 9.51. [α]D25 = 29.3 (c 10−3 g/mL, toluene). IR (cm−1): ν 2011 [vs, ν(SiH)], 1951 (m, sh), 1555 [s, ν(CN)]. 1H NMR (500 MHz, C6D6, 297 K): δ 5.83 (s, 1H, CH), 5.47 (d, 3JHH = 4.3 Hz, CHa), 5.46 (s, 1H, H4′), 5.38 (s, 1H, H4), 5.17 (m, 4H, SiHMe2), 5.01 (s, 1H, CHc), 3.82 (m, 4H, THF), 2.49 (s, 3H, Me3′), 2.45 (s, 3H, Me3), 2.22 (m, 4H, Hd,e,h), 2.05 (br s, 2H, Hg), 1.75 (s, 3H, Me5′), 1.66 (s, 3H, Me5), 1.40 (m, 4H, THF), 1.31, 1.00 (s, 6H, Mei,j), 0.58 (d, 3JHH = 2.7 Hz, 12H, SiHMe2), 0.53 (d, 3JHH = 2.8 Hz, 12H, SiHMe2). 13C{1H} NMR (125 MHz, C6D6, 297 K): δ 152.6, 150.9, 139.3, 138.6, 137.4 (C3,3′, C5,5′,Cb), 117.2 (Cc), 106.6 (CH4′), 105.9 (CH4), 81.6 (CHa), 71.8 (CH), 69.5 (THF), 58.8 (Cf), 41.1, 40.3, 36.9 (Cd,e,h), 31.5 (Cg), 26.1, 19.9 (Mei,j), 25.3 (THF), 14.4 (Me3′), 13.8 (Me3), 10.8 (Me5′), 10.3 (Me5), 4.0 (SiHMe2), 3.3 (SiHMe2). 29Si NMR (99.5 MHz, C6D6, 297 K): δ −22.9 (ds, 1JSiH = 178.0 Hz, 2JSiH = 8.2 Hz, NSiHMe2). Synthesis of [Y(κ3-bpzbe)2(O-bpzbe)] (7). In a 250 mL Schlenk tube, [Y(N(SiHMe2)2)3(thf)2] (0.50 g, 0.79 mmol) was dissolved in toluene (50 mL) and the solution was cooled to −50 °C. A solution of

Figure 7. (a) Plot of kobs versus concentration of 3 for the cyclization of (2-ethynylphenyl)methanol (13), showing first-order dependence on catalyst concentration. (b) Plot of log kobs versus log [3], confirming first-order dependence on catalyst concentration.

Figure 8. Plot of time dependence of substrate consumption for the cyclization of (2-ethynylphenyl)methanol (13) catalyzed by 3 at the indicated temperatures.

Figure 9. Arrhenius plot for the cyclization of (2-ethynylphenyl)methanol (13) catalyzed by 3 (5 mol %) over the temperature range 50−90 °C in toluene-d8. for C31H59N6O2Si4Y: C, 49.70; H, 7.94; N, 11.22. Found: C, 49.81; H, 7.81; N, 11.33. IR (cm−1): ν 2050 [vs, ν(SiH)], 1995 (m, sh), 1571 [s, ν(CN)]. 1H NMR (500 MHz, C6D6, 297 K): δ 7.23 (d, 3JHH = 7.4 Hz, 2H, Ho-MePh), 7.14 (d, 3JHH = 7.4 Hz, 2H, Hm-MePh), 5.89 (s, 1H, CH), 5.62 (s, 1H, CHa), 5.58 (s, 1H, H4′), 5.36 (s, 1H, H4), 5.31 (br s, 4H, SiHMe2), 3.81 (m, 4H, THF), 2.48 (s, 3H, Me3′), 2.47 (s, H


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Organometallics

(MePh), 17.7 (OMe2Ph), 13.4 (Me3′), 13.3 (Me3), 10.9 (Me5′), 10.2 (Me5). Synthesis of [Y(O-CH2(2-CHC)C6H4)2(κ3-bpzte)] (12). The synthetic procedure was the same as for complex 9, using complex 3 (0.50 g, 0.66 mmol), (2-ethynylphenyl)methanol (0.18 g, 1.33 mmol), and toluene (40 mL), to give 12 as a white solid. Yield: 0.40 g, 90%. Anal. Calcd for C37H37N4O3Y: C, 65.87; H, 5.53; N, 8.30. Found: C, 65.98; H 5.62; N, 8.11. 1H NMR (500 MHz, CDCl3, 297 K): δ 7.97 [br s, 2H, O-CH2(2-CHC)C6H4], 7.38 (d, 3JHH = 7.4 Hz, 2H, HoMePh), 7.29−7.03 [m, 8H, MePh, O-CH2(2-CHC)C6H4], 5.93 (s, 1H, CHa), 5.92 (s, 1H CH), 5.58 (s, 1H, H4′), 5.56 (s, 1H, H4), 4.87 [br s, 4H, O-CH2(2-CHC)C6H4], 3.24 [br s, 2H, O-CH2(2-CH C)C6H4], 2.34 (s, 3H, MePh), 2.31 (s, 3H, Me3′), 2.02 (s, 3H, Me3), 1.90 (s, 3H, Me5′), 1.61 (s, 3H, Me5). 13C{1H} NMR (125 MHz, CDCl3, 297 K): δ 151.0, 150.9, 140.4, 140.0, 139.4, 138.4, 137.9, 136.7, [C3,3′, C5,5′, Cipso,p-MePh, Cipso,o-O-CH2(2-CHC)C6H4], 131.4 (Cm-MePh), 126.1, 129.0, 128.7, 128.2, 125.3 [Co-MePh, O-CH2(2CHC)C6H4], 106.6 (CH4′), 105.2 (CH4), 80.6 [O-CH2(2-CH C)C6H4], 78.3 (CHa), 73.6 [O−CH2(2-CHC)C6H4], 70.3 (CH), 67.1 [O-CH2(2-CHC)C6H4], 21.4 (MePh), 13.4 (Me3′), 12.8 (Me3), 10.6 (Me5′), 10.3 (Me5). Synthesis of [Y{O-(CH2)3-(CC)TMS}2(κ3-bpzte)] (21). The synthetic procedure was the same as for complex 9, using complex 3 (0.50 g, 0.66 mmol) and 5-(trimethylsilyl)pent-4-yn-1-ol (0.21 g, 1.33 mmol) to give 21 as a white solid. Yield: 0.74 g, 90%. Anal. Calcd for C35H53N4O3Si2Y: C, 58.15; H, 7.39; N, 7.75. Found: C, 58.30; H, 7.61; N, 7.52. 1H NMR (500 MHz, CDCl3, 297 K): δ 7.26 (d, 3JHH = 8.3 Hz, 2H, Ho-MePh), 6.91 (d, 3JHH = 7.8 Hz, 2H, Hm-MePh), 6.27 (d, 3 JHH = 7.2 Hz, 1H, CH), 5.91 (d, 3JHH = 7.2 Hz, 1H, CHa), 5.61 (s, 1H, H4′), 5.45 (s, 1H, H4), 3.40, 2.16, 1.50 [m, 12H, O-(CH2)3-(C C)TMS], 2.13 (s, 3H, Me3′), 2.09 (s, 3H, Me3), 2.04 (s, 3H, MePh), 1.58 (s, 3H, Me5′), 1.46 (s, 3H, Me5), 0.21 [br s, 18H, O-(CH2)3(CC)TMS]. 13C{1H} NMR (125 MHz, CDCl3, 297 K): δ 148.0, 147.7, 140.4, 139.5, 137.2, 136.2 (C3,3′, C5,5′, Cipso,p-MePh), 128.5 (CmMePh), 127.0 (Co-MePh), 107.2 [O-(CH2)3-(CC)TMS], 106.3 (CH4′), 105.3 (CH4), 84.5 [O-(CH2)3-(CC)TMS], 74.9 (CHa), 74.3 (CH), 61.0, 31.3, 16.3 [O-(CH2)3-(CC)TMS], 20.7 (MePh), 13.4 (Me3′), 13.3 (Me3), 10.1 (Me5′), 9.9 (Me5), − 0.1 [O-(CH2)3(CC)TMS]. General Procedure for Catalytic Intramolecular Hydroalkoxylation. In a typical small-scale experiment, in a glovebox, 0.05 mmol (0.038 g) of catalyst [Y{N(SiHMe2)2}2(κ3-bpzte)(thf)] (3) and 1.00 mmol (0.132 g) of (2-ethynylphenyl)methanol (13) were dissolved in 0.75 mL of toluene-d8 and placed in a J. Young style NMR tube with a resealable Teflon valve. The tube was closed and placed in an oil bath that was preheated to the desired temperature. The reaction was monitored at regular intervals by 1H NMR spectroscopy to determine the optimum conversion. X-ray Crystallographic Structure Determination. Single crystals of 1, 2, and 7 were mounted onto a glass fiber using perfluoropolyether oil, and the X-ray intensity data were collected at 230 K on a Bruker X8 APEX II system using Mo Kα radiation (λ = 0.71073 Å). The system was equipped with an Oxford Cryosystems Cryostream Cooler Device. Data were integrated using the SAINT24 program, and the absorption correction was based on the symmetryequivalent reflections using SADABS.25 The space group determination was based on a check of the Laue symmetry and systematic absences and was confirmed by the structure solution. The structures were solved by direct methods using SHELXTL.26 All non-H atoms were located from successive Fourier maps, and hydrogen atoms were treated as a riding model on their parent carbon atoms. Anisotropic thermal parameters were used for all non-H atoms, and fixed isotropic parameters were used for H atoms, except the hydrogen atoms of silylamide ligands, which were freely refined. The three complexes 1a, 2b, and 7 show different quantities of toluene disordered about an inversion center. These toluene rings have been modeled as rigid bodies with two positions for each atom.

bpzbeH (0.69 g, 2.37 mmol) was added, and the reaction mixture was warmed to room temperature and stirred for 2 h. Evaporation of the solvent gave a white solid. The solid was recrystallized from toluene/ hexane (10/1, 30 mL at −20 °C) to give compound 7. Yield: 0.20 g, 27%. Anal. Calcd for C48H75N12O3Y: C, 60.24; H, 7.90; N, 17.56. Found: C, 60.35; H, 8.02; N, 17.48. 1H NMR (500 MHz, C6D6, 297 K): δ 6.07−4.00 (br s, 12 H, CH, H4, CHa), 2.50−0.90 [br s, 63H, Me, C(CH3)]. 13C{1H} NMR (125 MHz, C6D6, 297 K): δ 150.0−125.0 (br s, C3, C5), 106.6−65.0 (br s, CH4, CHa, CH), 35.5−10.0 [br s, C(CH3), Me]. Synthesis of [Y(κ3-bpzte)2(O-bpzte)] (8). The synthesis of 8 was carried out in in a manner identical with that for 7, using [Y(N(SiHMe2)2)3(thf)2] (0.50 g, 0.79 mmol) and bpzteH (0.81 g, 2.37 mmol). Complex 8 was isolated as a white solid. Yield: 0.20 g, 23%. Anal. Calcd for C57H69N12O3Y: C, 64.64; H, 6.57; N, 15.87. Found: C, 64.74; H, 6.97; N, 15.64. 1H NMR (500 MHz, C6D6, 297 K): δ 7.50−6.90 (br s, 12 H, Ph), 6.10−5.00 (br s, 12 H, CH, H4,4′, CHa), 2.50−1.50 (br s, 45 H, Me). 13C{1H} NMR (125 MHz, C6D6, 297 K): δ 150.0−125.0 (br s, C3, C5, Ph), 106.6−70.0 (br s, CH4,CHa, CH), 20.0−10.0 (br s, Me). Synthesis of [Y(O-2,6-Me2C6H3)2(κ3-bpzbe)] (9). To a stirred solution of complex 1 (0.50 g, 0.70 mmol) in cold (0 °C) toluene (20 mL) was added dropwise a solution of 2,6-dimethylphenol (0.17 g, 1.40 mmol) in toluene (20 mL). The reaction mixture was warmed to room temperature and was stirred for 1 h. The volatiles were removed under reduced pressure to afford compound 9. The solid was recrystallized from toluene/hexane (10/1, 20 mL at −20 °C) to give 9 as a white solid. Yield: 0.37 g, 85%. Anal. Calcd for C32H43N4O3Y: C, 61.93; H, 6.98; N, 9.03. Found: C, 62.09; H, 7.02; N, 8.88. 1H NMR (500 MHz, CDCl3, 297 K): δ 7.15 (d, 3JHH = 8.0 Hz, 4H, HmOMe2Ph), 6.72 (m, 2H, Hp-OMe2Ph), 6.25 (s, 1H, CH), 5.73 (s, 1H, H4′), 5.68 (s, 1H, H4), 4.98 (s, 1H, CHa), 2.45 (br s, 12H, OMe2Ph), 2.20 (s, 3H, Me3′), 2.18 (s, 3H, Me3), 2.10 (s, 3H, Me5′), 2.07 (s, 3H, Me5), 0.80 [s, 9H, −C(CH3)3]. 13C{1H} NMR (500 MHz, CDCl3, 297 K): δ 147.6, 147.2, 143.5, 141.2, 139.9, 120.1 (C3,3′, C5,5′, Cipso,oOMe2Ph), 126.5 (Cm- OMe2Ph), 125.6 (Cp- OMe2Ph), 106.5 (CH4′), 106.1 (CH4), 78.2 (CHa), 72.0 (CH), 34.6 [C(CH3)], 25.7 [C(CH3)], 17.1 (OMe2Ph), 13.1 (Me3′), 12.9 (Me3), 11.0 (Me5′), 10.9 (Me5). Synthesis of [Y(O-CH2(2-CHC)C6H4)2(κ3-bpzbe)] (10). The synthetic procedure was the same as for complex 9, using complex 1 (0.50 g, 0.70 mmol), (2-ethynylphenyl)methanol (0.19 g, 1.40 mmol), and toluene (40 mL), to give 10 as a white solid. Yield: 0.42 g, 93%. Anal. Calcd for C34H39N4O3Y: C, 63.75; H, 6.14; N, 8.75. Found: C, 63.85; H, 6.28; N, 8.59. 1H NMR (500 MHz, CD2Cl2, 297 K): δ 7.51− 7.25 [m, 8H, O-CH2(2-CHC)C6H4], 6.27 (d, 3JHH = 5.4 Hz, 1H, CH), 5.81 (s, 1H, H4′), 5.79 (s, 1H, H4), 4.95 (m, 1H, CHa), 4.81, 4.80 [s, 4H, O-CH2(2-CHC)C6H4], 3.40 [s, 2H, O-CH2(2-CH C)C6H4], 2.19 (s, 3H, Me3′), 2.17 (s, 3H, Me3), 2.10 (s, 3H, Me5′), 2.09 (s, 3H, Me5), 0.85 (s, 9H, -C(CH3)3], 13C{1H} NMR (500 MHz, CD2Cl2, 297 K): δ 147.6, 147.2, 143.5, 141.3, 139.9, 120.3 [C3,3′, C5,5′, Cipso,o-O-CH2(2-CHC)C6H4], 132.7, 129.1, 127.3, 127.1 [O-CH2(2CHC)C6H4], 106.8 (CH4′), 106.6 (CH4), 81.8 (CHa), 81.0 [OCH2(2-CHC)C6H4], 78.5 [O-CH2(2-CHC)C6H4], 72.0 (CH), 63.4 [O-CH2(2-CHC)C6H4], 34.6 [C(CH3)], 25.7 [C(CH3)], 13.1 (Me3′), 13.1 (Me3), 11.0 (Me5′), 10.9 (Me5). Synthesis of [Y(O-2,6-Me2C6H3)2(κ3-bpzte)] (11). The synthetic procedure was the same as for complex 9, using complex 3 (0.50 g, 0.66 mmol), 2,6-dimethylphenol (0.16 g, 1.33 mmol), and toluene (40 mL), to give 11 as a white solid. Yield: 0.38 g, 88%. Anal. Calcd for C35H41N4O3Y: C, 64.22; H, 6.31; N, 8.56. Found: C 64.41; H, 6.44; N, 8.25. 1H NMR (500 MHz, CDCl3, 297 K): δ 7.52 (d, 3JHH = 7.8 Hz, 2H, Ho-MePh), 7.42 (d, 3JHH = 7.8 Hz, 2H, Hm-MePh), 7.07 (d, 3JHH = 7.3 Hz, 4H, Hm-OMe2Ph), 6.57 (m, 2H, Hp-OMe2Ph), 6.24 (s, 1H, CH), 6.10 (s, 1H, CHa), 6.08 (s, 1H, H4′), 5.97 (s, 1H, H4), 2.30 (s, 3H, MePh), 2.21 (s, 3H, Me3′), 2.19 (s, 12H, OMe2Ph), 2.08 (s, 3H, Me3), 2.02 (s, 3H, Me5′), 1.80 (s, 3H, Me5). 13C{1H} NMR (500 MHz, CDCl3, 297 K): δ 162.9, 146.7, 146.1, 139.9, 139.1, 137.9, 136.5, 127.0, 126.8, 125.4, 125.2 (C3,3′, C5,5′, Cipso,p-MePh, Cipso,o- OMe2Ph), 128.2 (Cm-MePh), 126.9 (Cm-OMe2Ph), 126.7 (Co-MePh), 125.1 (CpOMe2Ph), 105.9 (CH4′), 104.9 (CH4), 73.7 (CHa), 71.9 (CH), 20.6 I


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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00203. Experimental details, procedures for catalytic intramolecular hydroalkoxylation, kinetic measurements and representative kinetic plots, and X-ray crystallographic data for complexes 1, 2, and 7 (PDF) X-ray crystallographic data for complexes 1, 2, and 7 (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*A.O.: e-mail, [email protected]; tel, +34926295300; fax, +34926295318. *A.L.-S.: e-mail, [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the Ministerio de Economı ́a y Competitividad (MINECO) of Spain (Grant Nos. CTQ2014-52899-R and CTQ2014-51912-REDC Programa Redes Consolider) and the Junta de Comunidades de Castilla-La Mancha of Spain (Grant No. PEII-2014-013-A).

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REFERENCES

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